1. Field of the Invention
The present invention relates to toner replenishment control for replenishing a containing unit with toner.
2. Description of the Related Art
There are image forming apparatuses that employ an electrophotographic method. This type of image forming apparatus forms a toner image based on image data input into the image forming apparatus, by consuming toner in a developer contained in a containing unit. It is known that, in this type of image forming apparatus, the density of the image formed by the image forming apparatus varies according to a ratio of the toner to the developer contained in the containing unit.
In this connection, one type of conventional image forming apparatuses predicts an amount of toner (a toner consumption amount) to be consumed in a containing unit due to formation of a toner image based on image data, and determines a toner replenishment amount so that a ratio of the toner in the containing unit becomes equal to a target value. Here, the toner consumption amount is theoretically obtained by calculation. Therefore, in reality, there is a slight error between a consumption amount of the toner actually consumed in the containing unit and the determined toner replenishment amount. In other words, the ratio of the toner in the containing unit may not become equal to the target value, even if toner is replenished based on the determined amount.
Japanese Patent Application Laid-Open No. 4-304486 discusses an image forming apparatus that corrects a toner replenishment amount according to a toner consumption amount, by using a correction amount calculated based on a ratio of toner in a containing unit.
In the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 4-304486, images each consuming a large amount of toner may be formed, after images each consuming a small amount of toner are formed, when the ratio of the toner in the containing unit is higher than a target value. In this case, the containing unit is not immediately replenished with the toner, which is a problem.
When the images each consuming a small amount of toner are formed in the case where the ratio of the toner in the containing unit is higher than the target value, the correction amount serves to suppress the toner replenishment amount. In other words, the correction amount is a negative value, when the ratio of the toner in the containing unit is higher than the target value.
Therefore, when the image consuming a large amount of toner is formed after the images each consuming a small amount of toner are formed, the toner replenishment amount becomes a value equal to or below 0. The toner replenishment amount is calculated based on the toner consumption amount predicted according to the image consuming a large amount of toner and the correction amount. Therefore, the containing unit is prevented from being replenished with the toner, even when formation of the image consuming a large amount of toner has commenced and the toner in the containing unit has started to decrease.